Vegetables and fruit such as apples, pears, tomatoes, citrus fruits and the like are selected in current practice on the basis of a large number of parameters, such as size, weight, color and the like. Because of increasing demands of consumers, there is now a trend toward also sorting fruits and vegetables according to hardness.
It is the current practice at auctions for an inspector to determine the hardness of a fruit in usually destructive manner by means of penetration with an impactor through about 2 cm. This hardness can have different values at different locations on the fruit. In the classification and selection of fruits there is therefore a need to determine the hardness of a fruit on the surface in non-destructive manner, for instance by means of non-destructive impact (or hardness) measurements.
In the international patent application PCT/GB98/01300 an impactor in a bellows is carried above one fruit or vegetable at a time, whereafter the local hardness derived from the elasticity is determined from the impact measured with a piezo-electric element.
This known method and device is however not suitable for performing measurements on fruits being supplied on a conveyor at a high speed, since the bellows must be brought close to the fruit each time. The hardness (or elasticity) of the fruit is furthermore determined at only one position, which provides an unreliable indication of the general hardness (and/or ripeness) of that fruit.
The present invention provides a method for determining the hardness of a vegetable or fruit, wherein the vegetable or fruit is rotated, wherein an impactor element is carried close to the surface of a fruit or vegetable, wherein during rotation of the fruit an impactor element is brought into contact with the fruit or the vegetable a number of times, wherein the impact of the respective impactor element is measured in order to determine the hardness of the vegetable or fruit over at least a portion of the surface thereof.
The impactor element preferably co-displaces with the fruit above the conveyor in order to enable a large number of measurements over the surface thereof while the fruit is supplied by the supply conveyor.
In another preferred embodiment of the method and device according to the present invention, it is likewise conceivable for a number of impactor elements to be in successive stationary disposition while the fruits are transported rotatingly thereunder (or over) on a conveyor. It is of course of equal importance here that the impactor elements can properly follow the contours of successive fruits or vegetables of perhaps differing diameter, for which purpose it is important that the impactor elements are freely movable in vertical direction.
The present invention further provides a device for determining the hardness of a vegetable or fruit, comprising:
a supply conveyor for supplying the vegetables or fruits,
rotation means for causing the vegetables or fruits to rotate on the supply conveyor; and
one or more hardness measuring members for measuring the hardness of the vegetables or fruits during rotation thereof, wherein the hardness measuring members are arranged above the supply conveyor.
In a further preferred embodiment of the device according to the present invention the hardness measuring members are arranged pivotally relative to each other or movable in height independently of each other in order to perform reliable hardness measurements on successive vegetables or fruits of different size.
In a first preferred embodiment the impactor element is lifted using a solenoid and then released, whereafter the impact thereof is measured using a piezo-electric transducer; in other embodiments mechanical lifting of the weight on the impactor element can also take place, wherein the impact is likewise determined by means of a piezo-electric transducer or with other means.
In a further preferred embodiment the hardness or impact transducer is arranged adjacently to a wheel or disc which rolls along the surface of a fruit and which, irrespective of the diameter thereof, prevents damage to this fruit. In the embodiment wherein the transducer co-displaces with the fruit, the hardness can be determined at any desired location along the surface, which increases the flexibility of the number of measurements and the speed of the conveyor.
The method and device according to the present invention can also be applied for other measurement principles, such as to determine the spectrum of the light reflected by the surface of a vegetable or fruit, the spectrum of the light passing through the object, the roughness of the skin of a vegetable or fruit, the analysis of the gases given off by the object and the like.
The present invention therefore also provides a method for determining a property of a vegetable or fruit, wherein the vegetable or fruit is rotated, wherein during rotation of the fruit the transducer is brought a number of times into the vicinity of the fruit or the vegetable, wherein the property is measured, in order to determine the property of a vegetable or fruit over at least a portion of the surface thereof.
The present invention further provides a device for performing such a method.
In order to prevent an (elongate) fruit which is supplied on a brush roller being forced laterally out of the conveyor path due to contact with a wheel or transducer, in accordance with another aspect the present invention provides a brush roller with one or more, preferably two, rings of slip-resistant material such as rubber. In a further preferred embodiment a sensor element or contact element is arranged between two diabolo-shaped elements in order to position the fruits properly and to obtain a reliable and accurate measuring result.